Method and apparatus of arrayed, clustered or coupled eddy current sensor configuration for measuring conductive film properties

Abstract

A method for minimizing measuring spot size and noise during film thickness measurement is provided. The method initiates with locating a first eddy current sensor directed toward a first surface associated with a conductive film. The method includes locating a second eddy current sensor directed toward a second surface associated with the conductive film. The first and second eddy current sensors may share a common axis or be offset from each other. The method further includes alternating power supplied to the first eddy current sensor and the second eddy current sensor, such that the first eddy current sensor and the second eddy current sensor are powered one at a time. In one aspect of the invention, a delay time is incorporated between switching power between the first eddy current sensor and the second eddy current sensor. The method also includes calculating the film thickness measurement based on a combination of signals from the first eddy current sensor and the second eddy current sensor. An apparatus and a system are also provided.

1 . A system for processing a wafer, comprising: 
 a chemical mechanical planarization (CMP) tool, the CMP tool including, 
 a wafer carrier defined within a housing, the wafer carrier having a bottom surface having a window defined therein;  
 a carrier film affixed to the bottom surface of the wafer carrier, the carrier film configured to support a wafer during CMP operations; and  
 a sensor embedded in the wafer the sensor disposed over a top surface of the window, the sensor configured to induce an eddy current in the wafer to determine a proximity and a thickness of the wafer;  
   a sensor array external to the CMP tool, the sensor array in communication with the sensor embedded in the wafer carrier, the sensor array including a first sensor and a corresponding second sensor, the first sensor and the corresponding second sensor configured to alternate between an active state and a passive state, the first sensor further configured to be in an active state when the second sensor is in a passive state, the sensor array configured to detect a wafer thickness signal that is independent of a distance of the first sensor and the corresponding second sensor to the wafer.    
   
   
       2 . The system of  claim 2 , wherein the first sensor and the corresponding second sensor of the sensor array have a common axis.  
   
   
       3 . The system of  claim 1 , wherein an axis of the first sensor is offset from an axis of the corresponding second sensor of the sensor array.  
   
   
       4 . The system of  claim 1 , wherein a signal from the first sensor is averaged with a signal from the corresponding second sensor to determine an initial thickness.  
   
   
       5 . The system of  claim 1 , further comprising: 
 a power supply in communication with both the first sensor and the corresponding second sensor; and    a controller configured to alternate power to the first sensor and the corresponding second sensor.    
   
   
       6 . The system of  claim 2 , wherein the controller is in communication with the embedded sensor and the sensor array, the controller configured to determine a thickness of the wafer from a signal provided by either the embedded sensor or the sensor array, the controller capable of providing a thickness profile of both a wafer prior to CMP and a wafer after CMP to a CMP controller.  
   
   
       7 . The system of  claim 1 , wherein the sensor array includes, 
 a plurality of top sensors;    a plurality of bottom sensors opposed to the top sensors, wherein each of the plurality of bottom sensors is coaxial with a corresponding one of the plurality of top sensors, the plurality of bottom sensors further configured to be passive when the corresponding one of the plurality of top sensors is active;    a power supply in communication with both the plurality of top sensors and the plurality of bottom sensors; and    a controller configured to alternate power from the power supply to the plurality of bottom sensors and the plurality of top sensors.    
   
   
       8 . The sensor array of  claim 7 , wherein the plurality of top sensors and the plurality of bottom sensors are eddy current sensors.  
   
   
       9 . The sensor array of  claim 7 , wherein the controller is further configured to incorporate a delay time when switching the sensors from a passive state to an active state.  
   
   
       10 . The sensor array of  claim 7 , wherein the sensor array is incorporated into an aligner station of a semiconductor processing tool.  
   
   
       11 . The sensor array of  claim 9 , wherein the delay time is 1 millisecond.